Monoclonal antibodies as immunospecific probes for virus and cell surface antigen localization with the unlabeled antibody hemocyanin bridge: a review.

Hemocyanin (Hcy) from whelks, Busycon canniculatum has been developed as a visual marker for the identification of virus and cell surface antigens by the correlative techniques of fluorescence microscopy, TEM and SEM. A series of hybridomas producing monoclonal antibodies that allow the identification of type-, group-, and class-specific antigenic determinants on the major envelope glycoprotein of mouse mammary tumor virus (MMTV) gp 52 and two group-specific monoclonal antibodies to MMTV gp 36 have been developed. We used these antibodies in the unlabeled antibody Hcy bridge for immunoelectron microscopy (IEM) and found that each gp 52 antigenic determinant was expressed on virus during all stages of morphogenesis and on the infected cell surface while the gp 36 determinants were not detected. The positive labeling of gp 52 by IEM correlated well with immuno-experiments using the 125I Staph protein A plate binding assay (125IPA). The anti-gp 36 monoclonals in contrast, however, gave positive results only in the 125IPA assay. Hybridomas to murine and primate type C virion envelope proteins [gp 70 and p15(E)] have also been developed. None of the monoclonal antibodies to murine type C virus gp 70 or p15(E) gave positive labeling by IEM when tested with Rauscher murine leukemia virus but two were positive by the 125IPA assay. Monoclonal antibodies to the gp 70 of a baboon type C virus, M-7 were positive in IEM, labeling both the cell surface and viral envelope and reacted with virus in the 125IPA assay. Since monoclonal antibodies provide a much better resolution of the molecular structure and antigenic differences of viruses, interpretations of labeling results are thoroughly discussed. Methods for testing the specificity and titer of monoclonals are presented. The unlabeled antibody Hcy bridge technique and recent advances in methodology are reviewed.